Composited cast member, iron-based porous substance for composited cast members, and pressure casing processes for producing the same, constituent member of compressors provided with composited cast members and the compressors

ABSTRACT

A pressure casing includes a composited cast member. The composited cast member includes an iron-based porous substance whose major component is Fe and which has a large number of pores, and a cast-wrapping member whose major component is a light metal and which cast-wraps a part of the iron-based porous substance at least. The iron-based porous substance includes a connector disposed adjacent to a boundary between the iron-based porous substance and the cast-wrapping member and exhibiting a larger porosity, and a high-strength reinforcer disposed in the iron-based porous substance free from the connector and exhibiting a smaller porosity. The connector is impregnated with the cast-wrapping member, and solidifies therewith, thereby firmly bonding the iron-based porous substance and the cast-wrapping member in the composited cast member. The pressure casing secures strength with the reinforcer, and secures adhesiveness with the connector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composited cast member in which an iron-based porous substance is wrapped with a light alloy, an iron-based porous substance used in the composited cast member, a pressure casing provided with the composited cast member, processes for producing the same, a constituent member of compressors, an example of the composited cast member or pressure casing, and the compressors.

2. Description of the Related Art

In view of weight saving, outputting higher power and recycling, raw materials for various component parts are changing from iron-based materials, such as iron, steels and cast steels, to light metallic materials, such as aluminum alloys and magnesium alloys. However, when such light alloy materials substitute for the entire component members, it is difficult to secure strength, rigidity, slidability, wear resistance and durability. Accordingly, composited cast products have been used which are made by cast-wrapping light-metal molten alloys around composite materials or iron-based component parts disposed only at parts which require a high sliding characteristic, for example. Note that the “composited cast member” set forth in the present specification includes the composited cast products. The composite materials comprise host materials composed of light metals, and reinforcement members, such as ceramic fibers and ceramic particles, dispersed in the host materials.

As for actual applications, there are the cylinder blocks of engines, especially, the cylinder liners. In the cylinder blocks, the weights have been saved by using aluminum cast products as the bodies, and simultaneously the required wear resistance and seizure resistance have been secured by using the aforementioned composite materials the cylinder liners or cast-wrapping sleeves made of cast steels with the composite materials.

However, it cannot necessarily be said that the weight saving of cylinder blocks is fully achieved when sleeves made of cast steels are cast-wrapped by light metallic materials. Moreover, in this instance, the adhesiveness is poor at the interface between cast-steel sleeves and cast-wrapping members composed of light metallic material, such as aluminum alloys, for example, and consequently the cast-steel sleeves and cast-wrapping members might be separated at the interface during the service as cylinder blocks. In order to satisfy the weight saving and adhesive requirements at the same time, iron-based porous substances have been disposed in aluminum alloy cast products, that is, iron-based porous substances have been cast-wrapped in aluminum alloy cast products. Japanese Unexamined Patent Publication (KOKAI) No. 7-124,738, Japanese Unexamined Patent Publication (KOKAI) No. 9-24,456, Japanese Unexamined Patent Publication (KOKAI) No. 2003-181,620 and Japanese Unexamined Patent Publication (KOKAI) No. 2003-181,622 deal with such technologies.

As for the applications of composite materials, Japanese Examined Patent Publication (KOKOKU) No. 63-40,943 sets forth the applications of composite materials to cylinder liners. Japanese Unexamined Patent Publication (KOKAI) No. 11-293,364 sets forth the applications of composite materials to the swash plates of swash type compressors.

In the case of composited cast members in which iron-based porous substances are cast-wrapped with cast-wrapping materials composed of light alloys, it is expected that the iron-based porous substances upgrade the strength of the composited cast members. When the porosity of iron-based porous substances is large, that is, when the volume fraction of iron (V_(f)) is less, such iron-based porous substances cannot demonstrate a sufficient reinforcement effect naturally. On the other hand, when the porosity of iron-based porous substances is small, that is, when the volume fraction of iron (V_(f)) is much, the strength of composited cast members upgrades, but cast-wrapping materials are less likely to impregnate into iron-based porous substances. Accordingly, the adhesiveness between iron-based porous substances and cast-wrapping members are likely to degrade. When separations occur between iron-based porous substances and cast-wrapping members, or when one of them comes off from the other, only iron-based porous substances are responsible for the strength substantially. Consequently, it is hardly possible to expect to strengthen composited cast members as a whole.

Japanese Unexamined Patent Publication (KOKAI) No. 7-124,738 and Japanese Unexamined Patent Publication (KOKAI) No. 9-24,456 suggest to add beryllium (Be) into molten metals in an appropriate amount in order to improve the adhesiveness. However, it is not preferable to add harmful Be. Japanese Unexamined Patent Publication (KOKAI) No. 2003-181,620 and Japanese Unexamined Patent Publication (KOKAI) No. 2003-181,622 disclose composited cast members in which porous substances made of stainless steels are cast-wrapped with aluminum alloys. However, the V_(f) of the porous substances is as low as from 10 to 30% by volume. As a result, although the resulting composited cast members can secure wear resistance as cylinder liners, it is hardly expected for the porous substances to produce the reinforcement effect as expected from composited cast members as a whole.

The use of composite materials is not suitable for mass-produced products which are required to be produced at low cost, because ceramic fibers, the reinforcement members, are expensive. Moreover, component parts using composite materials exhibit poor processability, because ceramic fibers are very hard.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the aforementioned circumstances. It is therefore an object of the present invention to provide a composited cast member in which an iron-based porous substance demonstrates the reinforcement effect fully while securing firm adhesiveness between the iron-based porous substance and a cast-wrapping member.

Moreover, it is another object of the present invention to provide an iron-based porous substance used in composited cast members, and a pressure casing provided with a composited cast member. It is a further object of the present invention to provide processes for producing the same. It is a furthermore object of the present invention to provide a constituent member of compressors, an example of pressure casings, and the compressors.

Hence, the present inventors have been studying earnestly in order to solve the problems, and have been repeated trials and errors. As a result, they have thought of changing the porosity of iron-based porous substances at parts thereof, iron-based substances which are cast-wrapped in cast-wrapping members. Based on the idea, they have arrived at completing the present invention.

(Composited Cast Member)

For example, a composited cast member according to the present invention comprises:

-   -   an iron-based porous substance comprising iron (Fe), and having         a large number of pores; and     -   a cast-wrapping member comprising a metal whose major component         is at least one member selected from the group consisting of         aluminum (Al) and magnesium (Mg), and cast-wrapping a part of         the iron-based porous substance at least;     -   the iron-based porous substance further comprising a connector         disposed adjacent to a boundary between the iron-based porous         substance and the cast-wrapping member and exhibiting a         predetermined porosity, and a high-strength reinforcer disposed         in the iron-based porous substance free from the connector and         exhibiting a porosity smaller than that of the connector; and     -   the connector being impregnated with the cast-wrapping member,         and solidifying therewith, thereby firmly bonding the iron-based         porous substance and the cast-wrapping member.

Note that the term, “metal,” herein means pure metals and alloy. Moreover, the compositions of the iron-based porous substance and cast-wrapping member depend on actual applications.

Firstly, the iron-based porous substance according to the present invention exhibits a large porosity at the connector making the boundary between the iron-based porous substance and the cast-wrapping member. Accordingly, when the iron-based porous substance is actually cast-wrapped in the cast-wrapping member, the connector is impregnated with a large amount of the molten metal of the cast-wrapping member, and solidifies therewith. As a result, a great anchor effect arises at least between the cast-wrapping member and the connector of the iron-based porous substance so that a mechanically firm bond is established between the iron-based porous substance and the cast-wrapping member. Of course, it is believed that a chemical bond might possibly be established between them. Anyway, the iron-based porous substance and the cast-wrapping member are bonded or joined firmly at the boundary of the iron-based porous substance which contacts with the cast-wrapping member directly. Consequently, separations are fully inhibited from occurring between the iron-based porous substances and cast-wrapping members, and one of them is also fully inhibited from coming off from the other.

Secondly, the iron-based porous substance according to the present invention comprises the reinforcer in addition to the connector. The reinforcer exhibits high strength, because it exhibits a smaller porosity and higher density, that is, because the V_(f) of the reinforcer is high. Therefore, the iron-based porous substance comprising the reinforcer can fully reinforce the cast-wrapping material of relatively low strength. Note that the reinforcer is disposed in the iron-based porous substance free from the connector, but all of the iron-based porous substance free from the connector cannot necessarily be turned into the reinforcer. As far as the strength required for composited cast members is secured depending on their applications, the position or proportion of the reinforcer do not matter. For example, when the entire surface of the iron-based porous substance is cast-wrapped by the cast-wrapping member completely, the connector can be disposed on the entire outer peripheral surface of the iron-based porous substance, and the reinforcer can be disposed at the center or in the middle of the iron-based porous substance. When only one of the opposite surfaces of the iron-based porous substance is cast-wrapped by the cast-wrapping member, the connector can be disposed on the opposite surface of the iron-based porous substance, and the reinforcer can be disposed on the other one of the opposite surfaces of the iron-based porous substance.

Thus, the present composited cast member fully secures the adhesiveness between the iron-based porous substance and the cast-wrapping member. Simultaneously therewith, the iron-based porous substance demonstrates the reinforcement effect stably and securely, because the iron-based porous substance comprises the high-strength reinforcer.

(Process for Producing Composited Cast Member)

It is possible to grasp the present invention not only as the above-described composited cast member but also as a process for producing the same. For instance, the present invention can be adapted to a process for producing a composited cast member, the process comprising the steps of:

-   -   impregnating an iron-based porous substance with a molten metal         for making a cast-wrapping member by pouring the molten meal         into a cavity of a mold in which the iron-based porous substance         is disposed, the iron-based porous substance comprising a         connector whose major component is Fe, having a large number of         pores and exhibiting a predetermined porosity, and a         high-strength reinforcer exhibiting a porosity smaller than that         of the connector, the molten metal comprising a metal whose         major component is at least one member selected from the group         consisting of Al and Mg, thereby impregnating the iron-based         porous substance with the molten metal inward from the connector         into the iron-based porous substance; and     -   solidifying the molten metal by cooling after the impregnating         step;     -   thereby producing a composited cast member in which the         iron-based porous substance is firmly bonded to the         cast-wrapping member at the connector, and is cast-wrapped by         the cast-wrapping member.

(Iron-Based Porous Substance for Composited Cast Members)

It is possible to grasp the present invention not only as the above-described composited cast member but also as an iron-based porous substance used in the same. For example, the present invention can be adapted to an iron-based porous substance comprising Fe, having a large number of pores and being cast-wrapped by a cast-wrapping member comprising a metal whose major component is at least one member selected from the group consisting of Al and Mg, and the iron-based porous substance further comprising:

-   -   a connector disposed adjacent to a potential boundary between         the iron-based porous substance and the cast-wrapping member,         and exhibiting a predetermined porosity; and     -   a high-strength reinforcer disposed in the iron-based porous         substance free from the connector, and exhibiting a porosity         smaller than that of the connector.

(Process for Producing Iron-Based Porous Substance for Composited Cast Members)

It is possible to grasp the present invention not only as the above-described iron-based porous substance for composited cast members but also as a process for producing the same.

(1) For instance, the present invention can be adapted to a process for producing an iron-based porous substance for composited cast members, the process comprising the steps of:

-   -   laminating a first powder compact exhibiting a predetermined         porosity, the first powder compact formed by pressing a ferrous         powder whose major component is Fe, on a second powder compact         exhibiting a smaller porosity than that of the first powder         compact, the second powder compact formed by pressing the         ferrous powder, thereby making a laminated powder compact; and     -   sintering the laminated powder compact, thereby producing an         iron-based porous sintered substance comprising a connector         formed of the first powder compact and exhibiting a         predetermined porosity, and a high-strength reinforcer formed of         the second powder compact and exhibiting a smaller porosity than         that of the connector.

In the present production process, the powder compacts whose porosities differ with each other are formed independently of each other. Accordingly, the degree of freedom enlarges in controlling the porosities, or in selecting raw materials to be used. As a result, the porosities or strengths can be controlled with ease depending on the parts of the resulting iron-based porous sintered substance, and consequently it is easy to produce the iron-based porous sintered substance whose porosity or strength is optimized. Note that the laminated powder compact produced after the laminating step and the iron-based porous sintered substance comprise two layers at least, but can naturally comprise three layers or more.

(2) Moreover, the present invention can be adapted to a process for producing an iron-based porous substance for composited cast members, the process comprising the steps of:

-   -   producing a powder compact by pressing a first powdery portion         comprising a mixture powder of a ferrous powder whose major         component is Fe and a pore-making material forming pores by         disappearing when being heated at temperatures of a sintering         temperature of the ferrous powder or less, and a second powdery         portion comprising the ferrous powder more than the first         powdery portion does and the pore-making material less than the         first powdery portion does; and     -   sintering the powder compact, thereby producing an iron-based         porous sintered substance in which the first powdery portion is         turned into a connector exhibiting a predetermined porosity and         the second powder portion is turned into a high-strength         reinforcer exhibiting a smaller porosity than that of the         connector.

In the present production process, the pore-making material is mixed abundantly in the portion (i.e., the first powdery portion) which is turned into the connector in the powder compact so that the portion is adapted to the connector whose porosity is larger after sintering. In the present production process, it is possible to readily control the porosity of the iron-based porous sintered substance produced after sintering by changing the mixing proportion of the pore-making material. Moreover, not only it is easy to control the porosity of the iron-based porous sintered substance, but also it is easy to control the strength of the iron-based porous sintered substance at parts thereof. In addition, the present production process is very efficient, because the forming step can be finished at once in the following manner. Specifically, the ferrous powder and pore-making material whose mixing proportions are changed at the parts of the resulting iron-based porous sintered substance are formed by simply pressing them immediately after filling them into the cavity of forming molds.

Note that, in the present production process as well, the mixing proportions of the ferrous powder and pore-making material can be changed stepwise not only in two stages but also in three stages or more. Moreover, the mixing proportions can be changed from the first powdery portion to the second powder portion gradiently. In addition, the second powdery portion can include a trace amount of the pore-making material, but the content of the pore-making material can be none.

The pore-making material herein can be metallic powders which exhibit melting points lower than the sintering temperature of the ferrous powder, or can be those which burn in high-temperature ranges (e.g., around the sintering temperature of the ferrous powder) and dissipate so that they can be removed by emission. For example, the former can be at least one member selected from the group consisting of Cu, Sn, Pb, Zn, Ag, Mg, Ca, Sr and Al powders, and the latter can be at least one member selected from the group consisting of binders, lubricants and resinous powders. Note that the phrase, “the pore-making material disappears,” means not only that the components of the pore-making material are removed out of the iron-based porous sintered substance completely, but also that the pore-making material melts to adhere onto the particulate surface of the ferrous powder or to diffuse into Fe, be taken therein or be alloyed therewith eventually.

(Pressure Casing)

It is possible to grasp the present invention as a pressure casing, an application of the above-described composited cast member. For example, a pressure casing according to the present invention, at least a part of the present pressure casing comprises a composited cast member, the composited cast member comprising:

-   -   an iron-based porous substance comprising Fe and having a large         number of pores; and     -   a cast-wrapping member comprising a metal whose major component         is at least one member selected from the group consisting of Al         and Mg and cast-wrapping a part of the iron-based porous         substance at least;     -   the iron-based porous substance further comprising a connector         disposed adjacent to a boundary between the iron-based porous         substance and the cast-wrapping member and exhibiting a         predetermined porosity, and a high-strength reinforcer disposed         in the iron-based porous substance free from the connector and         exhibiting a porosity smaller than that of the connector; and     -   the connector being impregnated with the cast-wrapping member,         and solidifying therewith, thereby firmly bonding the iron-based         porous substance and the cast-wrapping member.

The present pressure casing fully secures the adhesiveness between the iron-based porous substance and the cast-wrapping member in the same manner as the above-described composited cast member. Simultaneously therewith, the iron-based porous substance demonstrates the reinforcement effect stably and securely, because the iron-based porous substance comprises the high-strength reinforcer. Thus, the present pressure casing effects not only the advantages of weight saving but also sufficient strength.

The pressure casing according to the present invention can be pressure vessels, such as tanks and bombs, which hold highly pressurized fluids (e.g., gases and liquids) therein, can be cylinders for engines and compressors, or can be pipes for plumbing. The pressure casing forms an enclosed space as a whole, because it accommodates highly pressurized fluids therein. However, it is not required that the entire pressure casing comprises a single component part. For example, like cylinders or housings for engines and compressors, the pressure casing can comprise a cylinder-shaped component part (e.g., cylinder bore), a piston, a cylinder head or a valve plate to form the enclosed space. Note that any one of the component parts can comprise the present pressure casing.

However, a representative example of the present pressure casing can be cylinders themselves, or cylinder-shaped component parts, such as cylinder blocks and housings, which surround the cylinders. If such is the case, the present iron-based porous substance or the present pressure casing is adapted to cylinder-shaped component parts. In this instance, note that an internal pressure acts outward from the inner peripheral side of the pressure casing. Accordingly, in such cylinder-shaped component parts, the inner peripheral surface is likely to be subjected to the maximum stress. Consequently, the inner peripheral surface can preferably be reinforced by the reinforcer of the iron-based porous substance effectively. Therefore, it is appropriate that the iron-based porous substance of the present pressure casing can comprise the connector disposed on an outer peripheral side, and the reinforcer disposed on an inner peripheral side; and

-   -   the composited cast member comprises the iron-based porous         substance, and the cast-wrapping member cast-wrapping around the         connector of the iron-based porous substance.

(Process for Producing Pressure Casing)

Not limited to the above-described pressure casing, it is possible to grasp the present invention as a process for producing the same. For instance, the present invention can be adapted to a process for producing a pressure casing comprises the steps of:

-   -   impregnating an iron-based porous substance with a molten metal         for making a cast-wrapping member by pouring the molten meal         into a cavity of a mold in which the iron-based porous substance         is disposed, the iron-based porous substance comprising a         connector whose major component is Fe, having a large number of         pores and exhibiting a predetermined porosity, and a         high-strength reinforcer exhibiting a porosity smaller than that         of the connector, the molten metal comprising a metal whose         major component is at least one member selected from the group         consisting of Al and Mg, thereby impregnating the iron-based         porous substance with the molten metal inward from the connector         into the iron-based porous substance; and     -   solidifying the molten metal by cooling after the impregnating         step;     -   thereby producing a pressure casing partially provided with a         composited cast member in which the iron-based porous substance         is firmly bonded to the cast-wrapping member at the connector,         and is cast-wrapped by the cast-wrapping member.

(Constituent Member of Compressors)

A representative example of the above-described present pressure casing can be compressors and their constituent members. Hence, not limited to the present pressure casing using the present composited cast member, it is possible to grasp the present invention as a constituent member of compressors using the composited cast member.

For example, the present invention can be adapted to a constituent member of compressors which compress an intake working fluid and discharge the highly pressurized working fluid, at least a part of the constituent member comprising:

-   -   a composited cast member comprising:         -   an iron-based porous substance comprising Fe and having a             large number of pores; and         -   a cast-wrapping member comprising a metal whose major             component is at least one member selected from the group             consisting of Al and Mg, and cast-wrapping a part of the             iron-based porous substance at least;         -   the iron-based porous substance further comprising a             connector disposed adjacent to a boundary between the             iron-based porous substance and the cast-wrapping member and             exhibiting a predetermined porosity, and a high-strength             reinforcer disposed in the iron-based porous substance free             from the connector and exhibiting a porosity smaller than             that of the connector, the connector being impregnated with             the cast-wrapping member and solidifying therewith, thereby             firmly bonding the iron-based porous substance and the             cast-wrapping member in the composited cast member.

(Compressor)

Not limited to the above-described constituent member of compressors, it is possible to grasp the present invention as a compressor comprising the constituent member. For instance, the present invention can be adapted to a compressor which compress an intake working fluid and discharge the highly pressurized working fluid, at least a part of the constituent member comprising:

-   -   a composited cast member comprising:         -   an iron-based porous substance comprising Fe and having a             large number of pores; and         -   a cast-wrapping member comprising a metal whose major             component is at least one member selected from the group             consisting of Al and Mg, and cast-wrapping a part of the             iron-based porous substance at least;         -   the iron-based porous substance further comprising a             connector disposed adjacent to a boundary between the             iron-based porous substance and the cast-wrapping member and             exhibiting a predetermined porosity, and a high-strength             reinforcer disposed in the iron-based porous substance free             from the connector and exhibiting a porosity smaller than             that of the connector, the connector being impregnated with             the cast-wrapping member and solidifying therewith, thereby             firmly bonding the iron-based porous substance and the             cast-wrapping member in the composited cast member.

Note that the extent of porosity and the magnitude of strength according to the present invention are the relative relationships between the connector and reinforcer of the iron-based porous substance.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of its advantages will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings and detailed specification, all of which forms a part of the disclosure.

FIG. 1 is a perspective view for illustrating an outline of a housing of a compressor according to Example No. 1 of the present invention.

FIG. 2 is an enlarged view of the housing designated at “2” of FIG. 1.

FIG. 3 is a schematic diagram for illustrating an iron-based porous sintered substance according to Example No. 1 of the present invention, wherein FIG. 3(a) is the perspective view; and FIG. 3(b) is the cross-sectional view of the iron-based porous sintered substance along the center axis.

FIG. 4 is a metallographic photograph of a composited cast member according to Example No. 1 of the present invention, and shows a portion adjacent to a connector of the iron-based porous substance.

FIG. 5 is a side view for illustrating an outline of a housing according to Example No. 2 of the present invention for compressors.

FIG. 6 is a front view for illustrating an outline of a housing according to Example No. 3 of the present invention for compressors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Having generally described the present invention, a further understanding can be obtained by reference to the specific preferred embodiments which are provided herein for the purpose of illustration only and not intended to limit the scope of the appended claims.

The present invention will be hereinafter described in detail with reference to specific embodiments of the present invention. However, it should be noted that, not to mention the following descriptions on the specific embodiments, descriptions set forth in the present specification are appropriately applicable not only to the composited cast member according to the present invention but also to the iron-based porous substance, pressure casing and processes for producing the same according to the present invention, and further to the compressor and constituent members thereof according to the present invention. Moreover, it should be also noted that it depends on objects and performance requirements which one of the following specific embodiments is optimal.

(1) Iron-Based Porous Substance

The shapes and production processes of the present iron-based porous substance for composited cast members do not matter as far as the present iron-based porous substance comprises the connector and the reinforcer. A representative example of such an iron-based porous substance for composite cast members is iron-based porous sintered substances. One of the iron-based porous sintered substances will be hereinafter described in detail.

The iron-based porous sintered substance is made by sintering a powder compact comprising a ferrous powder. The powder compact is produced by pressing a ferrous powder filled in a cavity of molds. The composition of the ferrous powder used herein can be selected appropriately depending on the strength and service environments of the iron-based porous sintered substance. For example, when intending to upgrade the strength by heat treatments, it is advisable to use ferrous powders with the compositions of various alloy steels. When intending to enhance the corrosion resistance, it is advisable to use ferrous powders with the compositions of stainless steels. Additionally, the ferrous powder can be pure iron powders, or ferrous powders with the compositions of carbon steels. Note that the ferrous powder can be an independent single powder, or a mixture powder in which a plurality of powders are mixed.

The powder used herein can be either elemental powders or alloy powders. The types of using powder can be either atomized powders or reduced powders. The particulate shapes of using powder do not matter. Moreover, the compositions or types of the ferrous powder can be changed depending on parts of the iron-based porous sintered substance. In particular, when it is desirable to enlarge the porosity, it is not preferable to use fine powders having extremely small particle diameters. However, it is preferable to use a ferrous powder whose average particle diameter falls in a range of from 50 to 150 μm approximately, for instance. Note that the particle diameter of constituent particles can be determined by analyzing the two-dimensional images, but can be determined with ease by using sieving methods.

The ferrous powder is not limited to metallic powders, but can be mixture powders which include the above-described pore-making material in addition to lubricants and additives. Moreover, the ferrous powder can further include compound powders, such as powders composed of ceramic particles serving as reinforcement particles.

Note that the porosity of the iron-based porous sintered substance can be determined by the following equation using the apparent density p and the true density ρ₀of constituent materials: Porosity={1−(ρ/ρ₀)}×100(%)

For reference, the right side of the equation, {1−(ρ/ρ₀)}×100(%), specifies the volume fraction of the iron-based porous sintered substance (V_(f)).

It is appropriate that the porosity can fall in a range of from 20 to 50% by volume, more appropriately from 35 to 45% by volume, at the connector. When the porosity is to small, no sufficient adhesiveness is obtained because the bondability of the iron-based porous sintered substance was poor to the cast-wrapping member. It is difficult to produce iron-based porous sintered substances whose porosity is too large, and it is less likely to secure the strength for serving as the connector. On the other hand, the porosity of the reinforcer can appropriately fall in a range of from 5 to 25% by volume, more appropriately from 5 to 15% by volume. When the porosity of the reinforcer is too large, the strength of iron-based porous sintered substances degrades so that the reinforcer is less likely to demonstrate the reinforcement effect. Moreover, it is not efficient to make the porosity of the reinforcer too small, because it is required to press a raw material powder with high pressures.

(Process for Producing Iron-Based Porous Substance)

It does not matter that the present iron-based porous substance is produced by whatever production processes. Specifically, the present iron-based porous substance can be produced by the following production processes. For example, it is possible to use a process for producing an iron-based porous substance being cast-wrapped. This production process comprises the steps of:

-   -   laminating a first powder compact exhibiting a predetermined         porosity, the first powder compact formed by pressing a ferrous         powder whose major component is Fe, on a second powder compact         exhibiting a smaller porosity than that of the first powder         compact, the second powder compact formed by pressing the         ferrous powder, thereby making a laminated powder compact; and     -   sintering the laminated powder compact, thereby producing an         iron-based porous sintered substance comprising a connector         formed of the first powder compact and exhibiting a         predetermined porosity, and a high-strength reinforcer formed of         the second powder compact and exhibiting a smaller porosity than         that of the connector.

In the present production process, the powder compacts whose porosities differ with each other are formed independently of each other. Accordingly, the degree of freedom enlarges in controlling the porosities, or in selecting raw materials to be used. As a result, the porosities or strengths can be controlled with ease depending on the parts of the resulting iron-based porous sintered substance, and consequently it is easy to produce the iron-based porous sintered substance whose porosity or strength is optimized. Note that the laminated powder compact produced after the laminating step and the iron-based porous sintered substance comprise two layers at least, but can naturally comprise three layers or more.

Moreover, it is possible as well to use another process for producing an iron-based porous substance being cast-wrapped. For instance, the production process comprises the steps of:

-   -   producing a powder compact by pressing a first powdery portion         comprising a mixture powder of a ferrous powder whose major         component is Fe and a pore-making material forming pores by         disappearing when being heated at temperatures of a sintering         temperature of the ferrous powder or less, and a second powdery         portion comprising the ferrous powder more than the first         powdery portion does and the pore-making material less than the         first powdery portion does; and     -   sintering the powder compact, thereby producing an iron-based         porous sintered substance in which the first powdery portion is         turned into a connector exhibiting a predetermined porosity and         the second powder portion is turned into a high-strength         reinforcer exhibiting a smaller porosity than that of the         connector.

In the present production process, the pore-making material is mixed abundantly in the portion (i.e., the first powdery portion) which is turned into the connector in the powder compact so that the portion is adapted to the connector whose porosity is larger after sintering. In the present production process, it is possible to readily control the porosity of the iron-based porous sintered substance produced after sintering by changing the mixing proportion of the pore-making material. Moreover, not only it is easy to control the porosity of the iron-based porous sintered substance, but also it is easy to control the strength of the iron-based porous sintered substance at parts thereof. In addition, the present production process is very efficient, because the forming step can be finished at once in the following manner. Specifically, the ferrous powder and pore-making material whose mixing proportions are changed at the parts of the resulting iron-based porous sintered substance are formed by simply pressing them immediately after filling them into the cavity of forming molds.

Note that, in the present production process as well, the mixing proportions of the ferrous powder and pore-making material can be changed stepwise not only in two stages but also in three stages or more. Moreover, the mixing proportions can be changed from the first powdery portion to the second powder portion gradiently. In addition, the second powdery portion can include a trace amount of the pore-making material, but the content of the pore-making material can be none.

The pore-making material herein can be metallic powders which exhibit melting points lower than the sintering temperature of the ferrous powder, or can be those which burn in high-temperature ranges (e.g., around the sintering temperature of the ferrous powder) and dissipate so that they can be removed by emission. For example, the former can be at least one member selected from the group consisting of Cu, Sn, Pb, Zn, Ag, Mg, Ca, Sr and Al powders, and the latter can be at least one member selected from the group consisting of binders, lubricants and resinous powders. Note that the phrase, “the pore-making material disappears,” means not only that the components of the pore-making material are removed out of the iron-based porous sintered substance completely, but also that the pore-making material melts to adhere onto the particulate surface of the ferrous powder or to diffuse into Fe, be taken therein or be alloyed therewith eventually.

(2) Cast-Wrapping Member

The cast-wrapping member comprises at least one member selected from the group consisting of pure Al, Al alloys, pure Mg and Mg alloys. The compositions of alloys do not matter, however, it is possible to use various wrought alloys as stipulated in Japanese Industrial Standards. Appropriate alloys can be selected depending on the specifications of composite cast members, pressure casings and compressors. The following methods are available for casting: gravity casting; pressure casting; sand casting; and die casting, for example. However, it is preferable to carry out pressure casting using a mold, especially, liquid forging, in order to securely impregnate iron-based porous substances with molten alloys for making the cast-wrapping member. However, taking the mass-producibility into consideration, die casting can be used. The following solidifying step can be carried out by natural cooling. However, when cooling methods, such as water cooling, whose cooling rates are fast, the cast structure of the cast-wrapping member is micro-fined so that it is possible to upgrade the strength of the resulting composited cast member as a whole.

(3) Applications

The present composited cast member can be used in various component parts and apparatuses. In particular, the present composite cast member is appropriate for component parts which require higher strength than that of cast products comprising the cast-wrapping member alone, because the present composited cast member is reinforced by the iron-based porous substance. For example, such component parts can be cylinder blocks, various housings of compressors, bone structural component parts, inner shells or outer shells of pressure containers, and pipes for plumbing.

Note that, when the present composited cast member is adapted to component parts which are formed as cylinder shapes and are subjected to internal pressures, for instance, bulkheads of pressure vessels, the iron-based porous substance can appropriately be formed as a cylinder shape in which the connector is disposed on the outer peripheral side and the reinforcer is disposed on the inner peripheral side. This is because the maximum stress arises on the inner peripheral side of the present composited cast member or iron-based porous substance.

The present pressure casing can be adapted to cylinder sleeves, cylinder blocks and housing, which are used in pumps, compressors or engines, bulkheads, and pipes for plumbing, in addition to various pressure vessels. Note that the present compressor and its constituent members are some of specific embodiments of the present pressure casing.

EXAMPLES (Example No. 1) (Outline)

FIGS. 1 and 2 illustrate a cylinder-shaped housing 1 for compressors, Example No. 1 of the present invention. Note that the present composited cast member, constituent members of compressors or pressure casing include the cylinder-shaped housing 1. FIG. 2 is an enlarged view of an opposite end surface of the cylinder-shaped housing 1 designated at “2” in FIG. 1. Moreover, as illustrated in FIG. 1, the cylinder-shaped housing 1 is made on the assumption that an internal pressure “P” resulting from a working fluid acts outward from the inner peripheral side.

The housing 1 is a composited cast member which comprises a cylinder-shaped iron-based porous sintered substance 11, and a cast-wrapping member 12. The cast-wrapping member 12 is made by casting a casting aluminum alloy around the outer peripheral surface of the iron-based porous sintered substance 11. As illustrated in FIG. 2, the iron-based porous sintered substance 11 comprises a reinforcer 11 a, and a connector 11 b. The reinforcer 11 a is disposed on the inner peripheral side of the iron-based porous sintered substance 11, and exhibits a smaller porosity, that is, exhibits a larger V_(f). The connector 11 b is disposed on the outer peripheral side of the iron-based porous sintered substance 11, and exhibits a larger porosity, that is, exhibits a smaller V_(f). Moreover, the pores of the iron-based porous sintered substance 11 are impregnated with the molten metal for making the cast-wrapping member 12, and solidify therewith. In particular, in the pores disposed in the connector 11 b, the cast-wrapping member 12 has solidified firmly after the impregnation. Thus, the iron-based porous sintered substance 11 and the cast-wrapping member 12 are bonded firmly by an anchor effect.

(Production of Iron-Based Porous Sintered Substance)

The above-described cylinder-shaped iron-based porous sintered substance 11 was produced as hereinafter described. As raw material powders, the following powders were prepared: a reduced iron powder serving as the ferrous powder; graphite (C); stearic acid; a lubricant for powder metallurgy; and a copper powder. The reduced iron powder comprised pure iron, was “KIP240M” made by KAWASAKI SEITETSU Co., Ltd., and had an average particle diameter of 75 μm. The stearic acid had a melting point of 60° C. The lubricant was “W-02” made by DAIWA WAX Co., Ltd. The copper powder was “CE-5” made by FUKUDA KINZOKU Co., Ltd., and had an average particle diameter of 80 μm. These raw material powders were used to prepare a first mixture powder and a second mixture powder (i.e., mixing step). Note that the first mixture powder comprised 74% by mass Fe, 0.8% by mass C, and 3% by mass stearic acid. The second mixture powder comprised 87% by mass Fe, 0.8% by mass C, 2% by mass Cu, and 3% by mass stearic acid. Each of the first mixture powder and the second mixture powder was mixed for 1 hour using a milling apparatus.

The first mixture powder was filled into a cylinder-shaped cavity of a first mold (i.e., filling step), and was then formed by pressing (i.e., forming step). Thus, a first powder compact was produced whose inside diameter was φ 90 mm, outside diameter was φ 100 mm and length was 50 mm. The second mixture powder was filled into a cylinder-shaped cavity of a second mold (i.e., filling step), and was then formed by pressing (i.e., forming step). Thus, a second powder compact was produced which was fitted into the first powder compact and whose inside diameter was φ 80 mm, outside diameter was φ 90 mm and length was 50 mm. The resulting first powder compact (i.e., outer shell) and second powder compact (i.e., inner shell) were laminated by fitting the second powder compact into the first powder compact, thereby making a double-structured powder compact (i.e., laminating step).

The resultant powder compact was put in an electric furnace, and was sintered by heating it at 1,100° C. for 30 minutes in an inert or vacuum atmosphere (i.e., sintering step). Thus, the iron-based porous sintered substance 11 was produced whose inside diameter was φ 80 mm, outside diameter was φ 100 mm and length was 50 mm. The outer peripheral side of the iron-based sintered porous substance 11 comprised the sintered first powder compact, and exhibited a porosity of about 27% by volume. Note that the connector 11 b according to the present invention includes the outer peripheral side of the iron-based sintered porous substance 11. The inner peripheral side of the iron-based sintered porous substance 11 comprised the sintered second powder compact, and exhibited a porosity of about 13% by volume. Note that the reinforcer 11 a according to the present invention includes the inner peripheral side of the iron-based sintered porous substance 11. FIG. 3 illustrates schematically how the iron-based porous sintered substance 11 appeared. Note that FIG. 3(a) is the perspective view of the entire iron-based porous sintered substance 11; and FIG. 3(b) is the cross-sectional view of the iron-based porous sintered substance 11 along the center axis.

(Production of Composited Cast Member)

The iron-based porous sintered substance 11 was cast-wrapped with an aluminum alloy as per Japanese Industrial Standards 2024 which turned into the cast-wrapping member 12. Thus, a cylinder-shaped composited cast member, that is, the housing 1, was produced. The molten metal of the aluminum alloy was poured inward from the outer peripheral side of the iron-based porous sintered substance 11, that is, from the side of the connector 11 b. In this instance, the casting conditions were set so that the temperature of the molten metal was 750° C., the temperature of the mold was 200° C., the iron-based porous sintered substance 11 was preheated to 300° C., and the molten metal was pressurized to 100 MPa. Thus, the iron-based porous sintered substance 11 was impregnated with the molten metal of the aluminum alloy inward from the connector 11 b to the reinforcer 11 a. Thereafter, the mold was water-cooled to solidify the molten metal, thereby completing the cylinder-shaped composited cast member.

FIG. 4 shows a metallographic photograph of the composited cast member which was observed with an optical microscope after cutting the composited cast member adjacent to the connector 11 b and etching the cut cross section of the metallic structure with 3% alcoholic nitrate solution (or nital) for 15 seconds. From the metallographic photograph, it is appreciated that the pores of the connector 11 b was densely impregnated with the molten metal of the aluminum alloy and solidified therewith, and that the bonding was firm between the iron-based porous sintered substance 11 and the cast-wrapping member 12 (i.e., matrix).

Moreover, it is believed that the Cu powder (i.e., pore-making material), which had been mixed in the second powder compact, was melted by heat in the sintering and contributed to the formation of the pores in the connector 11 b. In addition, it is understood that the Cu powder itself melted in the sintering, flowed into voids made when the Fe powder was sintered, and filled the voids. Note that the composited cast member exhibited a tensile strength of from 535 to 564 MPa. The tensile strength was 546 MPa on the average when being measured three times.

(Example No. 2)

FIG. 5 illustrates a cylinder-shaped housing 2 for compressors, Example No. 2 of the present invention. Note that the present constituent members of compressors or pressure casing include the cylinder-shaped housing 2. The housing 2 was made by changing the shape of the iron-based porous sintered substance 11 in Example No. 1 to a trough-shaped iron-based porous sintered substance 21 whose cross section was formed as a semicircle, and by cast-wrapping the outer periphery of the iron-based porous sintered substance 21 with a cast-wrapping member 22. In Example No. 2, the inner peripheral side of the iron-based porous sintered substance 21 is turned into the reinforcer, and the outer peripheral side thereof is turned into the connector. Example No. 2 is effective when a high strength is required at the top of the inner peripheral side of the housing 2 in the drawing alone.

(Example No. 3)

FIG. 6 illustrates a cylinder-shaped housing 3 for compressors, Example No. 3 of the present invention. Note that the present constituent members of compressors or pressure casing include the cylinder-shaped housing 3. The housing 3 was made by changing the shape of the iron-based porous sintered substance 11 in Example No. 1 to a trough-shaped iron-based porous sintered substance 21 whose cross section was formed as a semicircle, and by cast-wrapping the inner periphery of the iron-based porous sintered substance 31 with a cast-wrapping member 32. In Example No. 3, the outer peripheral side of the iron-based porous sintered substance 31 is turned into the reinforcer, and the inner peripheral side thereof is turned into the connector. In Example No. 3, note that the iron-based porous sintered substance 31 was not disposed over the entire length of the housing 3, but was disposed in the middle of the housing 3 only. Example No. 3 is effective when a high strength is required at the top of the outer peripheral side of the housing 2 and in the middle thereof in the drawing alone.

Not limited to the above-describe examples, it is possible to think of a variety of many other examples depending on the types and specifications of compressors and the applications and forms of pressure casings.

Having now fully described the present invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the present invention as set forth herein including the appended claims. 

1. A composited cast member, comprising: an iron-based porous substance comprising iron (Fe), and having a large number of pores; and a cast-wrapping member comprising a metal whose major component is at least one member selected from the group consisting of aluminum (Al) and magnesium (Mg), and cast-wrapping a part of the iron-based porous substance at least; the iron-based porous substance further comprising a connector disposed adjacent to a boundary between the iron-based porous substance and the cast-wrapping member and exhibiting a predetermined porosity, and a high-strength reinforcer disposed in the iron-based porous substance free from the connector and exhibiting a porosity smaller than that of the connector; and the connector being impregnated with the cast-wrapping member, and solidifying therewith, thereby firmly bonding the iron-based porous substance and the cast-wrapping member.
 2. The composited cast member set forth in claim 1, wherein the connector exhibits a porosity of from 25 to 50% by volume, and the reinforcer exhibits a porosity of from 5 to 25% by volume.
 3. The composited cast member set forth in claim 1, wherein the porosity decreases from large to small in a gradient manner from the connector to the reinforcer.
 4. The composited cast member set forth in claim 1, wherein the iron-based porous substance comprises an iron-based porous sintered substance which is made by sintering a powder compact formed by pressing a ferrous powder whose major component is Fe.
 5. The composited cast member set forth in claim 1, wherein the iron-based porous substance is formed as a cylinder-shaped member in which the connector is disposed on an outer peripheral side and the reinforcer is disposed on an inner peripheral side, and the reinforcer is subjected to an internal pressure.
 6. A process for producing the composited cast member set forth in claim 1, the process comprising the steps of: impregnating an iron-based porous substance with a molten metal for making a cast-wrapping member by pouring the molten meal into a cavity of a mold in which the iron-based porous substance is disposed, the iron-based porous substance comprising a connector whose major component is Fe, having a large number of pores and exhibiting a predetermined porosity, and a high-strength reinforcer exhibiting a porosity smaller than that of the connector, the molten metal comprising a metal whose major component is at least one member selected from the group consisting of Al and Mg, thereby impregnating the iron-based porous substance with the molten metal inward from the connector into the iron-based porous substance; and solidifying the molten metal by cooling after the impregnating step; thereby producing a composited cast member in which the iron-based porous substance is firmly bonded to the cast-wrapping member at the connector, and is cast-wrapped by the cast-wrapping member.
 7. An iron-based porous substance used in the composited cast member set forth in claim 1, the iron-based porous substance comprising Fe, having a large number of pores and being cast-wrapped by a cast-wrapping member comprising a metal whose major component is at least one member selected from the group consisting of Al and Mg, and the iron-based porous substance further comprising: a connector disposed adjacent to a potential boundary between the iron-based porous substance and the cast-wrapping member, and exhibiting a predetermined porosity; and a high-strength reinforcer disposed in the iron-based porous substance free from the connector, and exhibiting a porosity smaller than that of the connector.
 8. A process for producing the iron-based porous substance set forth in claim 7, the process comprising the steps of: laminating a first powder compact exhibiting a predetermined porosity, the first powder compact formed by pressing a ferrous powder whose major component is Fe, on a second powder compact exhibiting a smaller porosity than that of the first powder compact, the second powder compact formed by pressing the ferrous powder, thereby making a laminated powder compact; and sintering the laminated powder compact, thereby producing an iron-based porous sintered substance comprising a connector formed of the first powder compact and exhibiting a predetermined porosity, and a high-strength reinforcer formed of the second powder compact and exhibiting a smaller porosity than that of the connector.
 9. A process for producing the iron-based porous substance set forth in claim 7, the process comprising the steps of: producing a powder compact by pressing a first powdery portion comprising a mixture powder of a ferrous powder whose major component is Fe and a pore-making material forming pores by disappearing when being heated at temperatures of a sintering temperature of the ferrous powder or less, and a second powdery portion comprising the ferrous powder more than the first powdery portion does and the pore-making material less than the first powdery portion does; and sintering the powder compact, thereby producing an iron-based porous sintered substance in which the first powdery portion is turned into a connector exhibiting a predetermined porosity and the second powder portion is turned into a high-strength reinforcer exhibiting a smaller porosity than that of the connector.
 10. A pressure casing, at least a part of the pressure casing comprising a composited cast member, the composited cast member comprising: an iron-based porous substance comprising Fe and having a large number of pores; and a cast-wrapping member comprising a metal whose major component is at least one member selected from the group consisting of Al and Mg and cast-wrapping a part of the iron-based porous substance at least; the iron-based porous substance further comprising a connector disposed adjacent to a boundary between the iron-based porous substance and the cast-wrapping member and exhibiting a predetermined porosity, and a high-strength reinforcer disposed in the iron-based porous substance free from the connector and exhibiting a porosity smaller than that of the connector; and the connector being impregnated with the cast-wrapping member, and solidifying therewith, thereby firmly bonding the iron-based porous substance and the cast-wrapping member.
 11. The pressure casing set forth in claim 10, wherein the iron-based porous substance and the composited cast member are formed as a cylinder-shaped member, respectively, and the pressure casing is subjected to an internal pressure exerted from an inner peripheral side of the composited cast member.
 12. The pressure casing set forth in claim 11, wherein the iron-based porous substance comprises the connector disposed on an outer peripheral side, and the reinforcer disposed on an inner peripheral side; and the composited cast member comprises the iron-based porous substance, and the cast-wrapping member cast-wrapping around the connector of the iron-based porous substance.
 13. A process for producing the pressure casing set forth in claim 10, comprising the steps of: impregnating an iron-based porous substance with a molten metal for making a cast-wrapping member by pouring the molten meal into a cavity of a mold in which the iron-based porous substance is disposed, the iron-based porous substance comprising a connector whose major component is Fe, having a large number of pores and exhibiting a predetermined porosity, and a high-strength reinforcer exhibiting a porosity smaller than that of the connector, the molten metal comprising a metal whose major component is at least one member selected from the group consisting of Al and Mg, thereby impregnating the iron-based porous substance with the molten metal inward from the connector into the iron-based porous substance; and solidifying the molten metal by cooling after the impregnating step; thereby producing a pressure casing partially provided with a composited cast member in which the iron-based porous substance is firmly bonded to the cast-wrapping member at the connector, and is cast-wrapped by the cast-wrapping member.
 14. A constituent member of compressors which compress an intake working fluid and discharge the highly pressurized working fluid, at least a part of the constituent member comprising: a composited cast member comprising: an iron-based porous substance comprising Fe and having a large number of pores; and a cast-wrapping member comprising a metal whose major component is at least one member selected from the group consisting of Al and Mg, and cast-wrapping a part of the iron-based porous substance at least; the iron-based porous substance further comprising a connector disposed adjacent to a boundary between the iron-based porous substance and the cast-wrapping member and exhibiting a predetermined porosity, and a high-strength reinforcer disposed in the iron-based porous substance free from the connector and exhibiting a porosity smaller than that of the connector, the connector being impregnated with the cast-wrapping member and solidifying therewith, thereby firmly bonding the iron-based porous substance and the cast-wrapping member in the composited cast member.
 15. A compressor, comprising: the constituent member set forth in claim
 14. 